Startup founders are naturally optimistic. They wouldn’t do it otherwise. But you should treat your optimism the way you’d treat the core of a nuclear reactor: as a source of power that’s also very dangerous. You have to build a shield around it, or it will fry you.

The shielding of a reactor is not uniform; the reactor would be useless if it were. It’s pierced in a few places to let pipes in. An optimism shield has to be pierced too. I think the place to draw the line is between what you expect of yourself, and what you expect of other people. It’s ok to be optimistic about what you can do, but assume the worst about machines and other people……

….The reason I warn startups not to get their hopes up is not to save them from being disappointed when things fall through. It’s for a more practical reason: to prevent them from leaning their company against something that’s going to fall over, taking them with it.

This advice is spot on, and I can’t count the times when I’ve found myself cautioning entrepreneurs not to be too optimistic. However, I’ve learned over the years that it’s hard advice to give. That’s because optimism is at once an asset and a potential weakness, as PG says. On the positive side optimism is a source of strength and motivation, particularly during difficult times, and it’s also a powerful aid to recruitment and sales – for these reasons it should be added to the list of cognitive biases of successful people. But on the negative side it can lead to bad business decisions when the chances of good outcomes are over-estimated.

I love the analogy with nuclear reactors because it makes it clear that optimism is a something to be loved and cherished, but that at the same time it needs to be contained and channeled to avoid danger.